1 Technical Field
This disclosure relates generally to an engine starting apparatus which is equipped with an inrush current reducer to reduce an inrush current drawn by an electric motor when energized.
2 Background Art
Usually, too large an inrush current flowing through an electric motor of an engine starter when starting an engine will result in a great drop in terminal voltage at a storage battery, which may cause electronic control units (ECUs) installed in a vehicle to be reset or operations of solenoid actuators to be unstable. In order to reduce the inrush current flowing through the electric motor, Japanese Patent First Publication No. 2009-224315 teaches installing an ICR (Inrush Current Reduction) relay with a built-in resistor in a power supply line leading to the electric motor.
Engine starters for use in idle-stop systems (also called automatic engine stop/restart systems) of automotive vehicles are required to minimize a period of time it takes to restart the engine (which will also be referred to as an engine restart time below) in order to ensure the comfort of a driver or passengers. The shortening of the engine restart time may be achieved by increasing the speed at which the engine is cranked. In order to achieve this along with the ensuring of startability of the engine at low temperatures where the mechanical friction of the engine is usually high, it is necessary to use a large-sized and high-power electric motor in the engine starter.
The increasing of speed at which the engine is cranked without use of the large-sized and high-power electric motor may be accomplished by switching operating characteristics of an electric motor installed in the engine starter between a high-speed mode and a high-torque mode. For instance, Japanese Patent First Publication No. 2004-197719 discloses techniques for using an electric motor equipped with a field coil made up of a series winding and a shunt winding and controlling a field current flowing through the shunt winding through an ECU to switch between the high-speed mode and the high-torque mode.
However, when the engine starter is placed in the high-speed mode to start the engine, the torque, as outputted by the engine starter, is usually low, thus resulting in a great increase in current flowing through the electric motor when the piston of the engine passes the top dead center for the first time. This current, as illustrated in FIG. 3, may exceed the value of inrush current, as decreased by the ICR relay, thus encountering the drawback in that the level of the inrush current is not kept below a permissible level.